1. Field of the Invention
This invention relates to silica based defoamer compositions having improved storage stability and their use in aqueous systems.
2. Description of the Prior Art
Silica based defoamers are well known as defoamers for aqueous systems. One of the problems of silica based defoamers, however, is the tendency of silica particles to settle out of the carrier liquid (usually a hydrocarbon or natural oil) in which they are suspended. Extremely fine particle silica can be used to provide stability, but fine particle silica is in limited supply and more expensive than other grades.
The following patents show the defoaming properties of various components in defoamer compositions but none teaches addition of hydrocarbon resins or fatty acids to improve shelf life of silica based defoamer compositions.
U.S. Pat. No. 3,076,768 (Boylan) describes silica base defoamers containing hydrophobic silica, hydrocarbon oil and a spreading agent.
U.S. Pat. No. 3,207,698 (Liebling and Canaris) describes silica base defoamers containing hydrophobic silica of a particular nature and hydrocarbon oil.
U.S. Pat. No. 3,697,440 (Lichtman and Woodward) describes defoamer compositions containing an oil insoluble polymer, a second oil insoluble or soluble polymer, a hydrocarbon oil and an amide.
U.S. Pat. No. 4,021,365 (Sinka and Lichtman) describes use of quick-chilled amides in silica based defoamer compositions to inhibit settling of silica particles.